For example, a liquid crystal display device is widely used in a display section of not only a clock or a calculator but also in a variety of measurement instruments, a vehicle, a word processor, an electronic diary, a printer, a computer, a television, a clock, an advertisement plate, or the like.
Examples of typical display methods of a liquid crystal display device include a twisted nematic (TN)-type method, a super twisted nematic (STN)-type method, an electrically controlled birefringence (ECB)-type method, and the like. In addition, in an active matrix-type liquid crystal display device in which a thin film transistor (TFT) is used, a VA-type driving method in which liquid crystal molecules are vertically aligned and an in-plane switch (IPS)-type driving method or a fringe field switching (FFS)-type driving method in which liquid crystal molecules are horizontally aligned are employed.
In recent liquid crystal display devices, for a variety of large-sized or small and medium-sized uses, an increase in definition and resolution such as 4K×2K or 8K×4K, an increase in display resolution such as 400 ppi or 600 ppi, and the like are carried out.
For liquid crystal display devices, an improvement of the optical response is one of the new problems required to be solved to make the liquid crystal display devices suitable for the above-described increases. Specifically, examples of a method for improving the optical response of a liquid crystal display device include the following means (1) to (5).
(1) To decrease the thickness of a liquid crystal layer
(2) To decrease the viscoelasticity of a liquid crystal material
(3) To improve the halftone response caused by application of overvoltage (referred to as overdrive method)
(4) To interpolate an image connecting movie frame by increasing the refresh rate (referred to as double speed drive)
(5) To drive a two-layer panel including a liquid crystal cell disposed at an optical compensation position under a specific condition (refer to NPL 1)
Meanwhile, in a liquid crystal display device, in order to achieve the above-described increase in definition, resolution, and display resolution, it is necessary to widen the viewing angle or improve color reproducibility and the like. Therefore, a number of research and development projects are underway at the moment.
As a useful method therefor, for example, there is a method in which a retarder (optical compensator) such as a negative A plate, a positive A plate, a negative C plate, a positive C plate, a biaxial plate, a half-wavelength plate, or a quarter-wavelength plate is used.
However, among these techniques, there are no techniques that improve the optical response using the design of a retarder (refer to PTLs 1 to 4). Therefore, regarding the method for improving the optical response of a liquid crystal display device, there have been no changes from the above-described way of thinking in the related art.
In addition, the response time of a liquid crystal display device with respect to a driving voltage is considered to follow Expressions A and B below which are solutions to a torque equation with respect to an external field. However, this way of thinking is not fundamentally wrong but is inaccurate.
                              τ          ⁢                                          ⁢          r                =                              y            ⁢                                                  ⁢            1            ⁢                          d              2                                                          Δ              ɛ                        ⁡                          (                                                V                  2                                -                                  Vth                  2                                            )                                                          Expression        ⁢                                  ⁢        A                                          τ          ⁢                                          ⁢          d                =                              y            ⁢                                                  ⁢            1            ⁢                          d              2                                                          n              2                        ⁢            K                                              Expression        ⁢                                  ⁢        B            
(In Expressions A and B, “τr” represents the response time during a rise time (ON), “τd” represents the response time during a fall time (OFF), “γl” represents the viscosity coefficient of a liquid crystal, “K” represents the elastic modulus of a liquid crystal, “d” represents the layer thickness of a liquid crystal, “Δ∈” represents the dielectric anisotropy of a liquid crystal, “V” represents a driving voltage, and “Vth” represents the threshold voltage.)
That is, Expressions A and B, accurately speaking, represent only the motion of a liquid crystal molecule and do not directly represent the temporal change in the amount of transmitted light through a liquid crystal display device. That is, the optical response of a liquid crystal display device can be considered as, for example, a time corresponding to a predetermined change in the amount of transmitted light when light passes through a pixel in a liquid crystal display device.
The amount of transmitted light through a liquid crystal display device is determined depending on the disposition of a polarization plate, the phase difference of a liquid crystal layer, the phase difference of a phase difference film, and the like. Therefore, Expressions A and B simply represent only the molecular movement in a liquid crystal layer and do not represent the temporal change in the amount of transmitted light which is directly related to the optical response of a liquid crystal display device.